Metal based redox reagents are used extensively in the chemical process industry (CPI) in organic homogenous reactions. The metal based redox reagents used by the CPI may be synthesized either chemically or electrochemically. Current CPI practice is to use a particular redox reagent once and then discard it, thus significantly increasing the cost for a particular manufacturing process.
Indirect electrochemistry has potential usefulness in the CPI because the redox reagents used in a particular chemical process are regenerated. The regenerated redox reagents can be reused for further homogenous chemical reactions, unlike conventional synthetic chemistry where the redox reagents are discarded after use. Thus, use of indirect electrochemistry could significantly lower overall chemical process costs. However, indirect electrochemistry has, as yet, found only limited application in the chemical process industry.
A reason for this limited use is that small amounts of organic contaminants, during the indirect electrochemical process, partition into the aqueous phase from the organic phase. These organic contaminants contact the surface of the electrode and thereby lower the electric current efficiency of regeneration of the redox reagent to levels which make indirect electrochemistry unattractive for use in CPI.
In the limited situations where indirect electrochemistry has been used in the CPI, various mass transfer steps have been employed to remove the organic contaminants from the aqueous phase prior to exposure of the aqueous phase to the electrode. These steps serve to lower the deleterious effects of the organic contaminants on the electric current efficiency of regeneration of the redox reagent. These steps include liquid-liquid separation of the aqueous phase from the organic phase before the aqueous phase reaches the electrode, cooling the aqueous phase before it reaches the electrode to crystallize, and thus remove, organic contaminants, and activated carbon adsorption of the organic contaminant from the aqueous phase. However, these additional steps can increase the complexity, as well as the cost, of the overall system and thus lower the viability of indirect electrochemistry as a useful tool to the CPI.
Another step which would diminish the deleterious effect of the organic contaminants would be to coat the electrode to inhibit passage of the contaminant to the electrode surface. Any coating of the electrode to inhibit passage of the organic contaminants from reaching the electrode surface would also inhibit the mass transport of the redox reagent to the surface of the electrode. Heretofore, no adequate coating has been recognized by the CPI which meets these two requirements.
Because of the long-term savings which would be realized if indirect electrochemistry were used in the CPI to regenerate redox reagents, there is a need to devise improved methods of indirect electrochemistry that would make indirect electrochemistry viable for use in the CPI. Such improvements would include ways to reduce the deleterious effect of organic contaminants on the electrode surface. Such improvements would allow indirect electrochemistry to be used in a variety of chemical synthesis applications which require homogenous chemical reactions with a redox reagent.